This invention relates to a communication device connected to a network, a communication system, and a communication control method, and more particularly, to a service-basis communication control method for a communication system adopting a protocol other than SIP, the communication system having a resource control device applied thereto.
The third generation mobile communication system is aimed to offer various multimedia services so as to provide, for example, voice, data, and moving image, of high quality at high speed. The 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2) are promoting standardization of “all IP-based mobile communication network” in order to provide multimedia service using an internet protocol (IP) technology on a packet switched network. The all IP-based mobile communication network is referred to, according to 3GPP, as IP multimedia subsystem (IMS), which is also referred to as multimedia domain (MMD) according to 3GPP2.
IMS relates to a technological specification of session control system which has been studied for establishing an all IP-based mobile communication network. According to IMS, a reference point is defined between the control network system and the transport network system, and the system is independent of the access network system. Accordingly, IMS is adopted into a session control technology in the next generation network (NGN).
According to IMS, session control is performed by a call state control function (CSCF), and subscriber information is held by a home subscriber server (HSS). Further, an application server (AP) provides an application.
According to the technology disclosed in “3GPP2 X. S0013-004-A v1.0, All-IP Core Network Multimedia Domain §4.6” (online), December 2005 (hereinafter, referred to as Non-patent Document 1), CSCF is broadly divided into three categories (P-CSCF, I-CSCF, and S-CSCF) according to the function thereof. P-CSCF (Proxy-CSCF) is accessed by a mobile terminal. I-CSCF (Interrogating-CSCF) specifies the S-CSCF of a mobile terminal. S-CSCF (Serving-CSCF) controls and manages a session state.
According to the technology disclosed in IETF RFC3261, “SIP: Session Initiation Protocol §4”, June 2002 (hereinafter, referred to as Non-patent Document 2), the session initiation protocol (SIP) is used as a session control protocol. SIP is a protocol for controlling a session of IP multimedia communication specified by IETF. An example of service using SIP is represented by voice over IP (VoIP). VoIP relates to a technology of transmitting and receiving voice information over an IP network. According to VoIP communication based on SIP, a virtual communication path (session) is set among communication devices before communication is started. Voice data formed into an IP packet is transferred over the set communication path. In the VoIP communication, SIP controls establishment, maintenance, and disconnection of a session among the communication devices.
Media information such as voice data is determined upon establishment of a session. The communication device notifies the media information based on session description protocol (SDP) included in an SIP message. According to SDP, it is possible to describe various information items (such as, for example, an IP address, a port number, and a media type) which relate to a session.
Further, 3GPP, 3GPP2, and NGN are studying a policy control mechanism on a service-by-service basis. In relation thereto, an outline of an operation for performing policy rule control when a session is established. Upon establishing an SIP session, CSCF and policy and charging rules function (PCRF) operate in association with each other, to thereby determine a policy for service which uses SIP protocol. PCRF notifies a policy determined as an access gateway (AGW, for example, PDSN). Then, the AGW applies the policy on a service-by-service basis.